Limiting the effects of inter-cell interference is an important factor for the performance of cellular radio communication systems. In Evolved—Universal Terrestrial Radio Access (E-UTRA) it is addressed specifically as Inter-cell interference mitigation. One of the discussed mitigation approaches is to avoid the use of the same frequency at the same time in neighbouring cells by co-ordination. According to E-UTRA, this inter-cell-interference co-ordination/avoidance may be defined for uplink in as: “The common theme of inter-cell-interference co-ordination/avoidance is to apply restrictions or preferences to the uplink scheduling, coordinated between cells. These restrictions can be in the form of restrictions to what time/frequency resources are available to the scheduler or restrictions on the transmit power that can be applied to certain time/frequency resources.”
This co-ordination can be applied on different time scales from classical static frequency reuse to fully synchronized schedulers between cells. The faster the co-ordination the better are interference variations from bursty packet data services and varying radio situations followed, and the larger is the potential improvement. Simulation results with a static frequency reuse shows no performance gain for a wideband packet data service, while a fully synchronized co-ordination without any delay indicates a large potential gain. Thus, the co-ordination method and protocols are important and specifically the resulting delay. The current assumption for E-UTRA is a co-ordination time scale of seconds but faster co-ordination is suggested.
In UTRA Enhanced UpLink (EUL) there is a downlink control channel Enhanced-Relative Grant CHannel (E-RGCH). It enables signalling from neighbouring cells within active set (cells having 3-5 dB pathloss difference) to a user equipment. When the uplink measured inter-cell interference is high, relative grants can be sent to the user equipment reducing the grant relatively the absolute grant from connected cell resulting in decreased transmission power.
Interference can also be measured resulting in indirect co-ordination if used in scheduling or on/off power control.
Uplink interference measures are also used for link adaptation and closed loop power control either direct or as measured C/I. Closed loop power control measures the received quality and adjusts the transmission power with a Transmit Power Command (TPC) to the transmitter.
Measured interference is delayed and is not able to capture bursty packet data transmissions. Measured interference is delayed and is not able to capture bursty packet data transmissions. When the interference is measured and action can be taken the interfering transmission is completed or close to be completed. This result in poor interference prediction degrading the performance of the algorithms based on interference measures.